Culture vessels, meaning containers for use in culturing cells and tissue growth, are well known. During typical growth or differentiation of cells, cells exhaust nutrients found in their growth media while simultaneously producing metabolic byproducts. Highly metabolic cell cultures may require replacement of the spent media with fresh media on a daily or bi-daily basis in order to replace nutrients and rid the culture of the byproducts.
A common approach for separating spent media involves first settling the cells, cells clusters, or micro-carriers to which the cells or cell clusters are attached to the bottom of the culture vessel. The spent media is then removed via suction or pumping through a straight tube with a hole at the distal-most end thereof, known as a diptube, submerged in the spent media using a pump. The goal of the process is to remove at least about 90% of the spent media, while removing as few cells as possible.
However, suctioning out of the media causes an upward pull directly above the settled cell layer. Additionally, an increase in pumping rate results in an increased pulling force above the cell layer. Thus, fast pump rates can disrupt the settled cell layer resulting in re-suspension of cell clusters, which re-suspended clusters are more likely to be removed as waste along with the spent media.
While fast pump rates may lead to the unintended removal of cells and cell clusters, pumping the media at too slow of a rate also can negatively impact the settled cell layer. Unlike cells in suspension, settled cells are in very close contact with each other and, when kept in a settled phase for a period of time, cell clusters may fuse to form larger cluster aggregates. Clusters with diameters larger than 200 μM may begin to experience gas and nutrient transport limitations. As a result, a sub-optimal differentiation or even cell death may be observed.